Patent Document 1 discloses an IGBT having trench gate electrodes that are bent when a semiconductor substrate is seen in a plan view. With the bent trench gate electrodes, as compared to linearly extending trench gate electrodes, a hole density increases in a drift region positioned inside the bent portions, which accelerates a conductivity modulation phenomenon and lowers an on-state voltage of the IGBT. It is noted that Patent Document 1 was not published at the time when the present application was filed.
In IGBTs, aside from a low on-state voltage, current between an emitter and a collector must be shut off when a voltage on the trench gate electrode is switched to an off-state voltage. A phenomenon in which current keeps flowing between the emitter and the collector even after the voltage on the trench gate electrode is switched to the off-state voltage is herein referred to as a “latchup”. It is necessary that no latchup should occur in IGBTs.